A heat pipe, such as a heat pipe described in Patent Document 1 (JPH11-23169), has been widely known. In the heat pipe, a heat transfer fluid is enclosed in a liquid-tightly closed metal pipe.
In the above-described configuration, the pipe needs to have high strength to enclose the heat transfer fluid. The volume of the heat transfer fluid increases when the heat transfer fluid is vaporized by the heat from a heat source, increasing the pressure in the pipe. The employment of the pipe that is configured to enclose a heat transfer fluid in a liquid-tightly closed state and has a relatively high strength requires a higher production cost.